If you can land a solid punch on the face and they are not expecting it you will knock almost anyone out-assuming your not a weak bitch-, the hard part is landing a solid punch to the face. Only place not to punch them would top of head or something as that be retarded and hurt your hand.

i've had the best luck w/ the blackspot. busted teeth through the upper lip and a likely broken nose = extreme pain and blurry vision. you'll also ko them if you get a good hit, and if you don't... finish em.

An overhand right to the chin, better if they can't see it coming. Connect well and it's lights out. Obviously some people are better conditioned to getting punched, so they may just laugh at you and turn the tables